A photocatalyst is generally employed in a state of a layer formed on the surface of an object, that is, a substrate for the purpose of oxidizing or decomposing substances which adhered to or contacted with the photocatalyst from the outside or for the purpose of disinfecting microorganisms. However, there is such a problem that the photocatalyst reacts with a substrate itself to oxidize or decompose it since the photocatalyst exerts a strong oxidizing action or decomposing action on the substrate.
As a method for forming a layer of a photocatalyst, a method wherein an active component (for example, titanium oxide) of a photocatalyst is applied or coated on the surface of a substrate by using a binder is known. In this method, however, excitation of the photocatalyst becomes weak since a coated film is formed even on the surface of the photocatalyst and thus reduction of the oxygen existing on the surface of the photocatalyst is delayed. On the other hand, there is a method wherein a photocatalyst is formed into a layer without using a binder so that an exposed surface of the photocatalyst is formed on the surface of a substrate. This method is preferable in the aspect of reaction efficiency with the photocatalyst since the more the active component of a photocatalyst is exposed on the surface of a substrate, the more readily the active component receives ultraviolet rays, and thus excitement of the photocatalyst is increased. However, when a layer of a photocatalyst is formed, for example, by a flame spray coating method to form an exposed surface of the photocatalyst on the surface of a substrate, minute spaces are produced among the particles of the active component of the photocatalyst in which spaces ultraviolet rays enter to cause problems such as oxidation and decomposition of the substrate.